Glass fibers having improved durability

ABSTRACT

A glass fiber and a method of manufacturing a glass fiber for reinforcing a transparent composite matrix is disclosed. The glass fiber includes a first glass material having a first refractive index, a first modulus, and a first durability characteristic and a second glass material having a second refractive index, a second modulus, and second durability characteristic. The second durability characteristic is greater than the first durability characteristic. Durability characteristic is selected from the group comprising resistance to chemical attack, resistance to acid attack, resistance to fading from exposure to ultra-violet radiation, and resistance to mechanical abrasion.

FIELD

The present disclosure is directed to transparent reinforcing materialsand reinforced composite materials, more particularly to transparentglass fibers used in composite materials and to a process for producingsuch fibers.

BACKGROUND

Transparent composite materials are known for use in vehicle and otherapplications requiring light transmission or visual transparency. Suchtransparent composite materials include windows or other transparentmaterials useful for light transmission there through, particularly inrugged environments and in locations requiring ballistic resistance.Such reinforcement further provides the window or transparent deviceresistance to cracking or breakage.

Transparent composite materials typically include a reinforcing fiber ina polymeric matrix. In order to render the composite materialtransparent, both the matrix material and the reinforcing fiber arefabricated from a transparent material. The materials are typicallyselected to include the same optical properties, thus minimizingdistortion.

The geometry of reinforcing fibers also affects the distortion impartedto the light passing through the transparent device. For example, roundfibers (i.e., fibers having circular cross-section) provide prismatic orother optical light refractive effects that provide overall distortionof the light passing through the transparent device.

These transparent composite materials are also required to withstandhigh impacts and structural loads, and thus are required to have highstrength and environmental durability. Environmental durability includesresistance to moisture, corrosion, ultra-violet (UV) light, solvents andother similar deleterious materials and conditions. The environmentaldurability of the composite is dependent upon the durability of both thematrix material and the reinforcing fibers. The term “durability” isintended to mean “environmental durability” for the remainder of thisdisclosure.

The reinforcing fibers are selected based on the required optical,strength, durability and cost requirements of the composite. However,often to meet optical, strength, and cost requirements, a fiber materialselected has a less than desirable environmental resistance ordurability, and in particular, resistance to chemical attack.

What is needed is a fiber reinforcing material having improveddurability at a reduced cost.

SUMMARY

A first aspect of the disclosure includes a glass fiber for reinforcinga transparent composite matrix comprising a first glass material havinga first refractive index and a first modulus, and a first durabilitycharacteristic, and a second glass material having a second refractiveindex, a second modulus, and second durability characteristic. Thesecond glass material coating the first glass material with asubstantially uniform coating layer, and the second durabilitycharacteristic is greater than the first durability characteristic.

A second aspect of the disclosure includes a method for fabricating aglass fiber for reinforcing a transparent composite matrix includingproviding a first glass fiber preform having a first refractive index, afirst modulus, and a first durability characteristic, coating the firstglass fiber preform with a second glass material having a secondrefractive index, a second modulus and a second durabilitycharacteristic to form a glass fiber preform having an initialcross-section with a preform total thickness; and hot working the glassfiber preform to reduce the initial cross-section to a finalcross-section having total thickness, a thickness of the first glassmaterial, and a substantially uniform coating thickness of the secondglass material. The second durability characteristic is greater than thefirst durability characteristic.

Other features and advantages of the present disclosure will be apparentfrom the following more detailed description of the preferredembodiment, taken in conjunction with the accompanying drawings whichillustrate, by way of example, the principles of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic cross-section view of a glass fiber accordingto an exemplary embodiment of the disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

“Transparent”, “transparency” and grammatical variations thereof includean ability of a material to permit passage of at least a portion oflight directed at the material, the term “light” including anywavelength range of interest, and more particularly to the visible, nearvisible and near infrared light ranges from about 380 nm to about 1000nm.

Referring to FIG. 1, a cross-section view of an exemplary glass fiber100 according to the disclosure is shown. As can be seen in FIG. 1,glass fiber 100 includes a first glass material 110 and a second glassmaterial 120. The glass fiber 100 has a generally rectangularcross-section having a total thickness T, first glass material thicknessT₁, a second glass material coating thickness T₂, and a width W. Thefirst glass material 110 and the second glass material 120 may both betransparent glass. In one embodiment, the first glass material 110 andthe second glass material 120 may both be transparent optical glass.

In alternative embodiments, the glass fiber 100 may have a differentcross-section geometry, for example, but not limited to generallysquare, generally oval, generally round and other similar geometries.

In one embodiment, the glass fiber 100 has a total thickness T ofbetween about 1 um to about 500 um with an aspect ratio of width W tototal thickness T of between about 5 and about 500. In anotherembodiment, the glass fiber 100 has a total thickness T of between about5 um and about 50 um with an aspect ratio of width W to total thicknessT of between about 10 and about 50.

In one embodiment, the second glass material coating thickness T₂ isbetween about 0.1% and about 100% the first glass material thickness T₁.In another embodiment, the second glass material coating thickness T₂may be between about 50 nm and about 5 um. In yet another embodiment,the second glass material coating thickness T₂ may be between about 50nm and about 1 um.

In another embodiment, the glass fiber 100 has a width W of betweenabout 5 um and 5000 um and an aspect ratio of width W to total thicknessT of between about 5 and about 500. In yet another embodiment, the glassfiber 100 has a width of between about 100 um to about 500 um and anaspect ratio of width W to total thickness T of between about 10 andabout 30.

The first glass material 110 is selected to have a first set of opticaland mechanical qualities, including, but not limited to a first RI, afirst Abbe number, a first transmission, a first modulus, a firstcoefficient of thermal expansion (CTE) and a first durabilitycharacteristic. The second glass material 120 is selected to have asecond set of optical and mechanical qualities including, but notlimited to a second RI, a second Abbe number, a second transmission, asecond modulus, a second CTE and a second durability characteristic. Thesecond durability characteristic is greater than the first durabilitycharacteristic.

Durability is measured by a material's resistance to chemical attack,resistance to acid attack, resistance to fading from exposure to UVradiation, and resistance to mechanical abrasion.

The second glass material 120 must be chemically compatible with thefirst glass material 110. Furthermore, the second glass material 120must not contain elements that will negatively affect the desirableproperties of the first glass material 110 during the method of formingthe glass fiber 100 or in the glass fiber 100.

Additionally, the second glass material 120 must be thermally compatiblewith the first glass material 110 to facilitate forming the fiber 100.For example, the second glass material 120 must have approximately thesame viscosity versus temperature profile at hot working temperatures asthe first glass material.

In one embodiment, the first glass material 110 is selected to have a RIapproximately equal to the RI of a polymeric material in which the glassfiber 100 is used to form a composite structure, such as a window. Inanother embodiment, the first RI is substantially different than thesecond RI. In yet another embodiment, the first RI is approximatelyequal to the second RI.

In one embodiment, the second glass material 120 has a modulus less thanthe modulus of the first glass material 110. In another embodiment, thesecond modulus is between about equal to and about 60% less than thefirst modulus.

In one embodiment, the second glass material 120 has approximately thesame optical performance as the first glass material 110. The secondglass material 120 may also have approximately the same viscosity versustemperature profile at hot working temperatures as the first glassmaterial 110 to facilitate forming the glass fiber.

In one embodiment, the second glass material 120 has a greater cost perpound than the cost per pound of the first glass material. In anotherembodiment the cost per pound of the second glass material may beapproximately the same as or less than the cost per pound of the firstglass material.

The glass fiber 100 may be formed by the following exemplary method.First, a first glass material preform of the first glass material isformed having a desired cross-section geometry and aspect ratio. Thecross-section of first glass material preform may be generallyrectangular, generally square, generally circular, generally oval, orother similar geometry. The first glass material preform may be formedby drawing, spinning, machining or other similar process.

The first glass material preform is then coated with a substantiallyuniform coating of the second glass material. The first glass materialmay be chosen for a desired optical performance. The second glassmaterial is chosen because of a greater durability characteristic ascompared to the same durability characteristic of the first glassmaterial.

The second glass material may be coated onto the first glass materialpreform by slumping, chemical vapor deposition, plasma vapor deposition,sol-gel processing, slurry coating, or other similar process.Alternatively, a coating of the second glass material may be formed onthe first glass material preform by modifying the surface composition ofthe first material preform by methods such as, but not limited to,reactive chemical diffusion. By forming the second glass material bymodifying the surface of the first glass material preform composition,the second material has a compositional gradient varying from that ofthe surface of the coated first glass material preform to the firstglass material preform composition. The material properties of themodified surface would also have a gradient from the properties of thesecond glass material at the surface to the properties of the firstglass material preform material at some predetermined distance from thesurface. The composition and property gradient may be abrupt or gradualin nature.

In one embodiment, the first glass material preform has a generallyrectangular cross-section having a thickness of between about 0.5 mm andabout 12.7 cm and an aspect ratio of width to thickness of between about5 and about 500.

In another embodiment, the second glass material coating thickness onthe first glass material preform is between about 1 um and 25.4 mm.

In another embodiment, the second glass material coating thickness isbetween about 0.1% and about 100% the thickness of the first glassmaterial preform.

The coated glass fiber preform is then drawn under heat and pressure bymethods well known in the art to form a glass fiber having a rectangularcross-section geometry having a total thickness, a first materialthickness, a second glass material coating thickness, and a width asdiscussed above. The glass fiber may be formed in a continuous,semi-continuous, or step process. In one embodiment, the coated glassfiber is provided as a stock material that is later drawn to form aglass fiber.

The glass fiber may be used with an epoxy resin or other polymericmaterial to form a composite structure, such as a window, by methodsappreciated by one of ordinary skill in the art.

In one embodiment, the formed glass fiber has a second glass materialcoating thickness of between about 0.1% and about 100% the thickness ofthe first glass material. In another embodiment, the second glassmaterial coating thickness may be between about 50 nm and about 5 um. Inyet another embodiment, the second glass material coating thickness maybe between about 50 nm and about 1 um.

In another embodiment, the formed glass fiber has a total thickness ofbetween about 1 um to about 500 um with an aspect ratio of width tototal thickness to width of between about 5 and about 500. In anotherembodiment, the formed glass fiber has a total thickness of betweenabout 5 um and about 50 um with an aspect ratio of width to totalthickness of between about 10 and about 50.

In another embodiment, the formed glass fiber has a width of betweenabout 5 um and 5000 um with an aspect ratio of width to total thicknessof between about 5 and about 500. In yet another embodiment, the glassfiber 100 has a width of between about 100 um to about 500 um and anaspect ratio of width to total thickness of between about 10 and about50.

The formed glass fiber includes a first glass material having a firstset of optical qualities, including, but not limited to a first RI, afirst Abbe number, a first transmission, a first modulus, a firstcoefficient of thermal expansion (CTE) and a first durability, and asecond glass material having a second set of optical qualitiesincluding, but not limited to a second RI, a second Abbe number, asecond transmission, a second modulus, a second CTE and a seconddurability. The second durability is greater than the first durability.

Durability characteristic is selected from a group comprising resistanceto chemical attack, resistance to acid attack, resistance to fading fromexposure to UV radiation, and resistance to mechanical abrasion.

The second glass material must be chemically compatible with the firstglass material. Furthermore, the second glass material must not containelements that will negatively affect the desirable properties of thefirst glass material during the method of forming the glass fiber or inthe glass fiber.

Additionally, the second glass material must be thermally compatiblewith the first glass material to facilitate forming the fiber. Forexample, the second glass material must have approximately the sameviscosity versus temperature profile at hot working temperatures as thefirst glass material.

In one embodiment, the first glass material has a RI approximately equalto the RI of a polymeric material in which the glass fiber 100 is usedto form a composite structure, such as a window. In another embodiment,the first RI is substantially different than the second RI. In yetanother embodiment, the first RI is approximately equal to the secondRI.

In one embodiment, the second glass material 120 has a modulus less thanthe modulus of the first glass material 110. In another embodiment, thesecond modulus is between about equal to and about 60% less than thefirst modulus.

In one embodiment, the second glass material 120 has approximately thesame optical performance as the first glass material 110. The secondglass material 120 may also have approximately the same viscosity versustemperature profile at hot working temperatures as the first glassmaterial 110 to facilitate forming the glass fiber.

In one example, a glass fiber is formed by selecting an optical glassN-SF66 produced by SCHOTT North America, Inc., of Elmsford, N.Y., as asecond glass material. This optical glass has a set of opticalproperties, including but not limited to an RI, an Abbe number, atransmission, a modulus and a durability including a high resistance toacid and a high climate resistance. This second glass material also hasa high cost per pound. A first glass material, having a lower durabilitybut at least one of a more desirable RI, Abbe number, or transmissionthan the second glass material, and also having a lower cost per poundrelative to the second glass material, is selected and a glass fiber isformed according to the above disclosure. The first glass material isselected to be chemically compatible with the first glass material.Additionally, the first glass material is selected to be thermallycompatible with the first glass material to facilitate forming the glassfiber. For example, the first glass material must have approximately thesame viscosity versus temperature profile at hot working temperatures asthe first glass material. It should be appreciated that the selection ofthe first glass material, which forms a greater portion of the glassfiber, having a lower relative cost compared to the second glassmaterial having improved durability, results in a substantial reductionin cost of the glass fiber compared to a glass fiber formed only of thesecond glass material, and results in a glass fiber having thedurability properties of the second glass material. Furthermore, theoptical properties of the formed glass fiber are substantially similarto the first glass material, because of the thin coating of the secondglass material contributing only slightly to the overall opticalqualities of the formed glass fiber.

In another example, a glass fiber is formed by selecting an opticalglass N-SK5 produced by SCHOTT North America, Inc., of Elmsford, N.Y.,as a first glass material. This optical glass has a set of opticalproperties, including but not limited to an RI, an Abbe number, atransmission, a modulus and a durability including a low resistance toacid and a low climate resistance. This first glass material also has alow cost per pound. A second glass material, having improved durabilitycompared to the first glass material, but also having a higher cost perpound relative to the second glass material, is selected and a glassfiber is formed according to the above disclosure. The second glassmaterial is selected to be chemically compatible with the first glassmaterial. Additionally, the second glass material is selected to bethermally compatible with the first glass material to facilitate formingthe glass fiber. For example, the second glass material must haveapproximately the same viscosity versus temperature profile at hotworking temperatures as the first glass material. It should beappreciated that the selection of the second glass material, which formsa lesser portion of the glass fiber, and having a higher relative costcompared to the first glass material, results in a substantial reductionin cost of the glass fiber compared to a glass fiber formed only of thesecond glass material. Furthermore, the optical properties of the formedglass fiber are substantially similar to the first glass material,because of the thin coating of the second glass material contributingonly slightly to the overall optical qualities of the formed glassfiber.

While the disclosure has been described with reference to a preferredembodiment, it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the disclosure. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the disclosure without departing fromthe essential scope thereof. Therefore, it is intended that thedisclosure not be limited to the particular embodiment disclosed as thebest mode contemplated for carrying out this disclosure, but that thedisclosure will include all embodiments falling within the scope of theappended claims.

1. A method for fabricating a glass fiber for reinforcing a transparentcomposite matrix, comprising: providing a first glass fiber preformforming a core having a first refractive index, a first modulus, and afirst durability characteristic; coating the core by contacting the corewith a second glass material having a second refractive index, a secondmodulus and a second durability characteristic to form a glass fiberpreform having an initial cross-section with a preform total thickness;and hot working the glass fiber preform to reduce the initialcross-section to a final cross-section having total thickness, athickness of the first glass material, and a substantially uniformcoating thickness of the second glass material, thereby forming glassfiber; forming a plurality of the glass fibers with a polymeric materialinto a transparent composite structure; wherein the second durabilitycharacteristic is greater than the first durability characteristic, thefirst and second durability characteristics being selected from thegroup consisting of resistance to chemical attack, resistance to acidattack, resistance to fading from exposure to UV radiation andresistance to mechanical abrasion; and wherein the first refractiveindex is approximately equal to the second refractive index.
 2. Themethod of claim 1 wherein the polymeric material has a third refractiveindex, the third refractive index being approximately equal to the firstrefractive index.
 3. The method of claim 1, wherein the durabilitycharacteristic is resistant to acid attack.
 4. The method of claim 1,wherein the final cross-section of the glass fiber has a substantiallyrectangular cross-sectional geometry.
 5. The method of claim 3, whereinthe glass fiber has a total thickness of between about 1 um to about 500um and an aspect ratio of width to total thickness of between about 5and about
 500. 6. The method of claim 1, wherein the second modulus isbetween equal to and about 60% less than the first modulus.
 7. Themethod of claim 1, wherein the hot working is selected from the groupcomprising extrusion, co-extrusion, hot drawing, spinning, andco-spinning
 8. The method of claim 1, wherein the glass fiber is formedwith a polymeric material into a composite window in which the polymericmaterial forms a matrix and the glass fiber reinforces the polymericmatrix.
 9. The method of claim 1, wherein the second glass material hasa greater cost per pound than the first glass material.
 10. The methodof claim 1 wherein the coating of the second glass material is appliedover the first glass fiber preform to provide a substantially uniformcoating thickness.
 11. The method of claim 10 wherein the coatingthickness is from about 50 nm to about 5 μm.
 12. The method of claim 1wherein the surface composition of the first glass fiber preform ismodified so that the second glass material is formed as a coating havinga compositional gradient varying from the composition of the first glassfiber preform at a predetermined distance from the surface to thecomposition of the second glass material at the surface.
 13. The methodof claim 12 wherein the material properties of the coating have agradient that varies from the material properties of the first glassfiber preform at a predetermined distance from the surface to thematerial properties of the second glass material at the surface.
 14. Atransparent composite structure formed by the process of claim
 1. 15. Atransparent composite structure, comprising: a first glass fiber preformhaving a first refractive index, a first modulus, and a first durabilitycharacteristic; a second glass material having a second refractiveindex, a second modulus and a second durability characteristicsubstantially uniformly coating the first glass preform to form a glassfiber having a cross-section with a total thickness comprising athickness of the first glass fiber preform, and the thickness of thesubstantially uniform coating thickness of the second glass material; apolymeric material having a third refractive index; wherein the glassfiber reinforces the polymeric material in the composite structure;wherein the second durability characteristic is greater than the firstdurability characteristic, the first and second durabilitycharacteristics being selected from the group consisting of resistanceto chemical attack, resistance to acid attack, resistance to fading fromexposure to UV radiation and resistance to mechanical abrasion; andwherein the first refractive index is approximately equal to the secondrefractive index.
 16. The composite structure of claim 15 wherein thethird refractive index is approximately equal to the first refractiveindex.